Folded dipole antenna with internally mounted loading means



Feb. 14, 1961 s x 2,972,146

FOLDED DIPOLE ANTENNA WITH INTERNALLY MOUNTED LOADING MEANS Filed July29, 1959 INVENTOR HAROLD A. SAXE BY {7% M.

ATTORNEY United States Patent Ofitice 2,972,146 Patented Feb. 14, 1961FOLDED DIPOLE ANTENNA WITH INTERNALLY MOUNTED LOADING MEANS Harold A.Saxe, Whippany, N.J., assignor to Western Electric Company,Incorporated, New York, N.Y., a corporation of New York Filed July 29,1959, Set. No. 830,281

2 Claims. or. 343-749 This invention relates to a folded dipole antennaand more particularly to a folded dipole antenna having loading circuitsmounted therein.

An object of the invention is to provide a new and improved foldeddipole antenna.

Another object of the invention is the provision of a folded dipoleantenna having loading circuits to physically shorten the elements forpermitting operation of a parasitic array where wind velocities orlimited space prohibit the use of full-length beams.

A further object of the invention is to provide a folded dipole antennawhich offers improved radiation eificiency, harmonic suppression andweather resistance.

Apparatus illustrating certain features of this invention may include aprimary and a secondary active means for transmitting and receivingelectromagnetic waves. The secondary active means includes two spaced,axially aligned members mounted parallel to and insulated from theprimary means. Loading circuits are connected between the ends of theactive means.

More particularly apparatus illustrating certain features of theinvention may include a primary tubular active element, and a pair ofloading circuits respectively mounted within, and insulated from, theouter ends of the primary element. One terminal of each of the circuitsis connected electrically to each of the ends of the primary element. Apair of secondary active elements are fixed to and insulated from theprimary element, the secondary elements being axially aligned with theircommon axis parallel to the axis of the primary element. The otherterminal of each of the circuits is connected electrically to each ofthe outer ends of the secondary elements to complete an electrical pathbetween the primary element and the secondary elements.

A complete understanding of the invention may be had from the followingdetailed description of a specific embodiment thereof when read inconjunction with the appended drawing, in which:

Fig. 1 is a front elevational view of a preferred embodiment of theantenna;

Fig. 2 illustrates an enlarged fragmentary sectional view of a portionof Fig. l; and

Fig. 3 shows an enlarged sectional view taken along line 33 of Fig. 2.

Referring to the drawing, wherein like reference characters designatelike or corresponding parts throughout the several views, there is shownin Fig. l a folded dipole antenna,-designated generally by the numeral11, having a primary tubular active element 12 and a pair of axiallyaligned and spaced secondary tubular elements 13. The secondary elements13 are of a smaller diameter than and fixed spatially to the primaryelement 12 by insulated connectors 14 so that the common axis of thesecondary elements 13 is spaced from, and parallel to, the axis of theprimary element 12. Of course, the diameter, length and spacing ofelements 12 and 13 may be varied in accordance with desired impedance,directional and radiating properties.

Loading coils, designated generally by the numeral 15, including awinding 16 and a core 17 (Figs. 2 and 3) of an insulating material, suchas hard rubber or the like, are mounted removably within the outer endsof the primary element 12. The core 17 is fixed to a disk 18 of aninsulating material, such as hard rubber, which may be fitted removablywithin an annular member 19 to form a weather-tight seal between themember 19 and the disk 18. The annular member 19 may be of the samematerial as the primary element 12 and is fitted removably within it -toform a weather-tight seal between the element 12 and the member 19, thuseffectively sealing the ends of the element 12.

One end of the winding 16 is fixed to the annular member '19 by weldingor the like, While the other end of the winding 16 is engaged to thesecondary element 13 by means of a threaded member 21 (Figs. 2 and 3).Hence, it is apparent that the loading coil 15 may be replaced simply byremoving the annular member 19, the disk 18, and substituting the coil15 with a different coil having an impedance characteristic as desired.

A transmitting or receiving unit, not shown, to be used in conjunctionwith the antenna is connected electrically thereto by leads 22, Fig. 1.

'For antenna physical lengths of one-fourth wave length or less, it isadvisable to use tuned circuits of lumped constants at the ends of theelements to improve radiation efliciency. Since the tuned circuit wouldbe positioned within one of the elements 12 or 13, it would be protectedfrom weather conditions, thereby maintaining the antenna resonancevirtually constant under extreme temperature and humidity changes.Alternatively, the ends of the folded dipole antenna 11 may be loaded byshort loops of wire or other conductive material insulated and placedinside the radiating elements 12 or 13.

The loading coils 15, or other loading circuits, provide an inductive orcapacitive load which simulates a short or an open circuit, depending onthe frequency applied to, and the length of, the elements 12 and 13.Consequently, the use of the loading coils 15 causes the radiation ofharmonic frequencies to be reduced and most of the antenna resonantfrequencies to be harmonically unrelated. Hence, the antenna 11 may beused for multiband operation on frequencies which are not exactmultiples of the lowest frequency. It may also be used as a single bandantenna capable of limiting harmonic radiation.

Also, the antenna loading may be adjusted for operation on frequencieswhich either are or are not exact multiples of the lowest tunedfrequency of the antenna. By electrically loading the ends of theantenna rather than loading its center, a larger portion of antennaradiation current can be utilized in signal transmission.

It should be understood that the loading coils 15 may be positionedwithin the secondary elements 13 if the size of the coils 15 andelements 13 permit.

It should be further understood that the above-described embodiment ofthe invention is merely illustrative and that numerous modifications maybe made within the spirit and scope of the invention.

What is claimed is:

1. In a folded dipole antenna having a hollow elongated active elementand a loading circuit mounted therein, a loading circuit support formounting within the active element which comprises a core of insulatingmaterial, an insulating disk fixedly engaged to the core, and aconductive annular member coaxially surrounding the disk, the annularmember being of a size for reception within the end of the activeelement such that the core and the loading circuit are sealinglydisposed completely within the element.

2. In a folded dipole antenna having hollow elonmaterial, an insulatingdisk fixedly engaged to the core and having an aperture formedtherethrough, and a conductive annular member coaxially surrounding thedisk for connection to one end of the loading circuit to be supported,the other end of the circuit being disposed sea-lingly through theaperture formed through the disk 10 2,744,248

and connected electrically to the secondary active element, the annularmember being of a size for reception within the end of the primaryactive element such that the core is sealingly disposed completelywithin the element.

References Cited in the file of this patent UNITED STATES PATENTS WarrenFeb. 7, 1933 Ehrbar et al. Jan. 12, 1954 Cupec May 1, 1956

